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ECLinPS circuit performance at non-standard VIH levels

Posted: 06 Dec 2000     Print Version  Bookmark and Share

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4-1 REV 0) Motorola, Inc. 1996 5/92 AN1404 Application Note This application note explains the consequences of driving an ECLinPS device with an input voltage HIGH level (VIH) which does not meet the maximum voltage specified in the ECLinPS Databook. ECLinPSTM Circuit Performance at Non Standard VIH Levels Prepared by Todd Pearson ECL Applications Engineering ECLinPS is a trademark of Motorola, Inc. AN1404 MOTOROLA ECLinPS and ECLinPS Lite DL140 -- Rev 3 4-2 ECLinPS Circuit Performance at Non-Standard VIH Levels Introduction When interfacing ECLinPS devices to various other technologies times arise where the the input voltages do not meet the specification limits outlined in the ECLinPS data book. The purpose of this document is to explain the consequences of driving an ECLinPS device with an input voltage HIGH level (VIH) which does not meet the maximum voltage specified in the ECLinPS Databook. The results outlined in this document should not be viewed as guarantees by Motorola but rather as representative information from which the reader can base design decisions. It is up to the reader to assess the risks of implementing the non-standard interface and deciding if that level of risk is acceptable for the system design. Motorola's guarantee on VIH will continue to be the specification standards established for the 10HTM and 100K ECL technologies. Overview The upper end of the VIH spec of an ECLinPS, or any other ECL, input is limited by saturation affects of the input transistor. Figure 1 below illustrates a typical ECL input (excluding pulldown resistors and ESD structures); the structure is a basic differential amplifier configuration. With a logic HIGH level asserted at the input the collector of that transistor will be pulled down below the VCC rail by the gate current passing through the collector load resistor. The voltage at the collector of the input transistor (VC) will be dependent on the gate current and the size of the collector load resistor associated with the input gate. Figure 1. Typical ECLinPS Input Structure VCC VC VBBInput VCB As the input VIH increases towards VCC the collector base junction of the input transistor becomes forward biased; as this forward bias condition increases the transistor will move into the saturation region. The value of VCB at which the transistor begins to saturate is process dependent and will vary from logic family to logic family. Fortunately the MOSAIC III process used to implement the ECLinPS family incorporates a deep n+ collector doping. This deep collector helps to mitigate the effects of saturation of transistors by requiring a larger collector-base forward bias to enter the saturation region. VIHmax and the ECLinPS Family As previously mentioned the MOSAIC IIITM process allows for ECLinPS devices to operate at VIHmax levels somewhat higher than those specified in the databook, however the exact value of VIH for which saturation problems will occur varies from device to device and even among different inputs for a given device. This variation is a result of the differentinput configurations used on the various inputs of ECLinPS devices. The easiest way to define an acceptable VIHmax for each device in the family is to define at what point the input transistor will saturate and specify for each input what the worst case input transistor collector voltage will be. With this information designers will be able to determine on a part by part, input by input basis what input voltage levels will be acceptable for their application. Simulation Results The input saturation phenomenon was characterized through SPICE simulations and the results will be reported in the following text. For simplicity of simulation a buffer similar to the E122 was used. Since the outputs of this buffer drive off chip, the VIHmax performance of this structure will be worse than the typical input structure. Both a 100K and a 10H style buffer were analyzed to note any discrepancies between the two standards. As expected the simulation results showed no difference in the saturation susceptibility of a 100K versus a 10H style buffer. Therefore the simulation results of only the 100K style buffer will be presented to minimize redundancy of information. The following text will refer to Figures 4-8 in the appendix of this document. Figures 4-8 are graphical plots of the input and output waveforms of an E122 style buffer (structure similar to that of Figure 1) for various VIH levels. V(in) represents the input voltage while V(q) and V(qb) represent the output voltages. The V(vbb) line was included for measurement purposes only and will be ignored. Figure 4 represents the "standard" operation of the device as a standard VIH input was used. Note that in this condition the propagation delays measure in the 215-225ps range and the IINH was 42.55A. The IINH of this device is simply a measure of the base current of the input transistor when that transistor is conducting current. We will be monitoring both of these conditions as well as any degradation in the output waveforms as a sign of the input transistor becoming saturated. As can be seen in Figures 5 and 6 none of the parameters change for VIH levels of up to -0.4V. With a collector voltage, VC, of -1.0V these VIH's correspond to a collector base forward bias of 600mV. As the VIH of the input moves closer to VCC, Figures 7 and 8, three phenomena start to occur: the IINH increases, the delays increase and significant changes occur to the output low level of the QB pin. AN1404 4-3 MOTOROLAECLinPS and ECLinPS Lite DL140 -- Rev 3 In Figure 7 the IINH of the input transistor has more than doubled from the "standard" level. This increase in base current leads to an increase in the VOL level as the collector current must reduce to maintain the constant emitter current. As the collector current reduces, the IR drop across the collector load resistor reduces, thus raising the VOL level on the QB output. Although the VOL level has shifted the overall propagation delay has remained essentially unchanged. Finally, when the input is switched all the way up to VCC the VOL level no longer remains in spec as the input base current has jumped to almost 1ma and there has been significant degradation in the high-low propagation delay. It is apparent that for this condition an E122 style buffer will not perform adequately for most systems. From this information it can be concluded that for a collector-base forward bias of 600mV there will be no adverse conditions on the performance of the device. The performance starts to degrade with further forward bias until at a forward bias voltage of 1.0V the device will fail both its DC and AC specifications. ECLinPS Input Structures There are four basic input structures which will affect the VIHmaxperformanceofECLinPSdevices.Thefourstructures are as follows: an internal buffer, an external buffer, an emitter follower input buffer and a series gated emitter follower input. The internal buffers are input structures whose outputs drive other gates internal to the device, the voltage swings of the input transistor collectors (VC) on these devices will be 800mV. An external buffer is one in which the outputs are fed external to the chip. Because of the relatively large base drive of the output emitter follower for these structures the VC voltage will typically be a couple hundred milivolts lower than for the internal buffer. Note that because of the larger output swings of a 10E device, a 10E style external buffer will require a VIHmax input level more near the specified value. Both of these structures are similar to that pictured in Figure 1. The third and fourth structures are somewhat different in design than the first two. Figure 2 illustrates an emitter follower input structure. For the basic emitter follower input the input voltages are dropped by an additional VBE (800mV) beforethey are fed into the differential amplifier input gate. The switching reference is also shifted down by one diode drop to remain centered in the input swing. Obviously this input structure will represent the "best case" in the area of extended VIHmax performance. In fact this type of input structure will allow for input voltages even several hundred millivolts above the VCC rail. This characteristic makes these type devices ideal for interfacing with differential oscillators whose outputs lack any DC offset. In the emitter follower structure the limiting factor will be the saturation of the emitter follower device whose collector is at VCC. From the previous simulation results this would suggest a maximum VIH of +0.6V. Figure 2. Emitter Follower Input Structure VCC VC VBBInput VCB VCB VBB' The series gate emitter follower input will represent the absolute worst case situation for a 100E device. Figure 3 represents a series gate emitter follower input for a 10E and a 100E device. From this figure it is apparent that the lower switching level (B input level) is going to be much more susceptible to VIHmax for the 100E device than the 10E device. The two diode drops used for the 10E device is not possible for a 100E device due to the smaller VEE voltage of a 100E device. To summarize the external gate will represent the worst case VIHmax situation for a 10E device while the series gate emitter follower case will represent worst case for a 100E device. In either situation the standard emitter follower will allow the most leeway for non-standard VIHmax performance. Figure 3. Emitter Follower Series Gate Input Structure VCC VC VBBInput A VCB VBB' VCB Input B VCB VCC 100E Structure VCC VC VBBInput A VCB VBB'' VCBInput B VCB VCC 10E Structure AN1404 MOTOROLA ECLinPS and ECLinPS Lite DL140 -- Rev 3 4-4 Other Considerations When driving ECLinPS devices with other than standard input levels there is another phenomena that should be considered; namely effects of non-centered switching references on the AC performance of a device. For non-standard input voltages the midpoint of the voltage swing may not correspond to the internal VBB switching reference. If this is the case the resulting AC variation should be included in the evaluation of a design. An input voltage swing not centered about the switching reference will exhibit a delay skew between the two input edge transitions. The size of this skew will be dependent on both the voltage offset of the reference voltage and the midpoint of the input swing and the slew rate of the input as it passes through the threshold region. As an example for the case in which the VIH = -0.5V and the VIL remains at -1.7V the midpoint of the swing will be at -1.1V versus a -1.32V VBB reference. With a typical slew rate of 1ps/mV for ECLinPS type edge rates the rising input edge delay will be 220ps longer than normal and the falling edge delay will be 220ps faster. This results in a 440ps skew between the two input transitions that would not be seen for an ideal switching reference. The only means of correcting this skew is to lower the VIL level to recenter the swing or provide a different switching reference for the device. The latter can be accomplished by buffering the signal with a differential input device with one input tied to an externally generated switching reference. Raising the VIL level is not recommended due to the obvious loss of low end noise margin accompanied by any such shift. Conclusions Simulations show that forward bias levels of 600mV on the input transistor will keep the input transistor in the active region and the performance of the device will not be compromised. This forward bias voltage can be increased with varying degrees of performance degradation to levels somewhat higher than 600mV. Initial effects will be an increase in the IINH current and a decrease in the output VOL level on the QB output of the input gate. As the forward bias increases further the propagation delays through the device will be adversely affected. The following example will outline the use of the table in the appendix to analyze the potential performance of a design using non-standard VIH levels. If a design called for the 10E112 and the 10E416 to be driven by a -0.2V input signal a designer would want to know if these two devices would perform to specifications under these conditions. From the table the worst case collector voltage VC would be -1.05V and 0.0V respectively. Subtracting these values from -0.2V yields forward bias voltages of 850mV and -200mV respectively. From this information the designer would conclude that the 10E416 will function with no problems however the 10E112 could suffer performance degradation under these same conditions. The device information contained in the appendix of this document will provide designers with all of the information necessary to evaluate the input transistor forward bias conditions for all of the ECLinPS devices for different input voltages. With these numbers and the information provided in this document designers will be able to make informed decisions about their designs to meet the performance desired at an acceptable level of risk. 10H and MOSAIC III are trademarks of Motorola, Inc. AN1404 4-5 MOTOROLAECLinPS and ECLinPS Lite DL140 -- Rev 3 Appendix Device Input Input Structure VC (10E Typical) (V) VC (10E Worst Case) (V) VC (100E Typical) (V) VC (100E Worst Case) (V) E016 E101 E104/107 E111 E112 E116 E122 E131 E141 E142 E143 E150 E151 E154 E155 E156 E157 E158 E160 E163 E164 E166 E167 E171 E175 E195 E196 E212 E241 E256 E336 E337 E404 E416 E431 E451 E452 E457 All All Dna Dnb All Dn EN/ All All D Other All All All Dn Other All All All All Dn SEL Dn SEL R, CLK Other All All All All All All All All All All All All All All All All All All Dn SEL INT EF EXT SG INT EXT INT EXT EXT INT SG INT INT INT EXT INT INT INT INT INT EXT INT EXT INT SG INT INT INT INT INT INT INT INT INT INT INT INT INT INT EF EF INT INT INT EF INT -0.80 -0.15 -0.95 -0.50 -0.80 -0.95 -0.80 -0.95 -0.95 -0.90 -0.50 -0.80 -0.80 -0.80 -0.95 -0.80 -0.80 -0.80 -0.80 -0.80 -0.95 -0.80 -0.95 -0.80 -0.50 -0.80 -0.80 -0.80 -0.80 -0.80 -0.80 -0.80 -0.80 -0.80 -0.80 -0.80 -0.80 -0.80 -0.80 0.00 0.00 -0.80 -0.80 -0.80 0.00 -0.80 -0.90 -0.25 -1.05 -0.60 -0.90 -1.05 -0.90 -1.05 -1.05 -1.00 -0.60 -0.90 -0.90 -0.90 -1.05 -0.90 -0.90 -0.90 -0.90 -0.90 -1.05 -0.90 -1.05 -0.90 -0.60 -0.90 -0.90 -0.90 -0.90 -0.90 -0.90 -0.90 -0.90 -0.90 -0.90 -0.90 -0.90 -0.90 -0.90 0.00 0.00 -0.90 -0.90 -0.90 0.00 -0.90 -0.80 -0.10 -0.90 -1.20 -0.80 -0.90 -0.80 -0.90 -0.90 -0.90 -1.20 -0.80 -0.80 -0.80 -0.90 -0.80 -0.80 -0.80 -0.80 -0.80 -0.90 -0.80 -0.90 -0.80 -1.20 -0.80 -0.80 -0.80 -0.80 -0.80 -0.80 -0.80 -0.80 -0.80 -0.80 -0.80 -0.80 -0.80 -0.80 0.00 0.00 -0.80 -0.80 -0.80 0.00 -0.80 -0.90 -0.20 -1.00 -1.30 -0.90 -1.00 -0.90 -1.00 -1.00 -1.00 -1.30 -0.90 -0.90 -0.90 -1.00 -0.90 -0.90 -0.90 -0.90 -0.90 -1.00 -0.90 -1.00 -0.90 -1.30 -0.90 -0.90 -0.90 -0.90 -0.90 -0.90 -0.90 -0.90 -0.90 -0.90 -0.90 -0.90 -0.90 -0.90 0.00 0.00 -0.90 -0.90 -0.90 0.00 -0.90 INT = Internal Gate; EXT = External Gate; EF = Emitter Follower Input; SG = Series Gated Input AN1404 MOTOROLA ECLinPS and ECLinPS Lite DL140 -- Rev 3 4-6 0 4000 TIME 2000 -2.25 -2.0 -1.75 -1.5 -1.25 -1.0 -0.75 -0.5 -0.25 V(VBB) V(QB) V(Q) V(IN) VOLTAGE Figure 4. Input and Output Waveforms for VIH = -0.9 (VOL = -1.8; TPD++ = 215ps; TPD- - = 225ps; IINH = 42.55A) Figure 5. Input and Output Waveforms for VIH = -0.5 (VOL = -1.8; TPD++ = 204ps; TPD- - = 207ps; IINH = 43.45A) 0 4000 TIME 2000 -2.0 -1.75 -1.5 -1.25 -1.0 -0.75 -0.5 -0.25 -0.0 VOLTAGE V(VBB) V(QB) V(Q) V(IN) AN1404 4-7 MOTOROLAECLinPS and ECLinPS Lite DL140 -- Rev 3 Figure 6. Input and Output Waveforms for VIH = -0.4 (VOL = -1.8; TPD++ = 201ps; TPD- - = 206ps; IINH = 46.75A) Figure 7. Input and Output Waveforms for VIH = -0.3 (VOL = -1.8; TPD++ = 196ps; TPD- - = 198ps; IINH = 114.85A) VOLTAGE 0 4000 TIME 2000 -2.0 -1.75 -1.5 -1.25 -1.0 -0.75 -0.5 -0.25 -0.0 V(VBB) V(QB) V(Q) V(IN) VOLTAGE 0 4000 TIME 2000 -2.0 -1.75 -1.5 -1.25 -1.0 -0.75 -0.5 -0.25 -0.0 V(VBB) V(QB) V(Q) V(IN) AN1404 MOTOROLA ECLinPS and ECLinPS Lite DL140 -- Rev 3 4-8 Figure 8. Input and Output Waveforms for VIH = 0.0 (VOL = -1.8; TPD++ = 196ps; TPD- - = 287ps; IINH = 9125A) VOLTAGE 0 4000 TIME 2000 -2.0 -1.75 -1.5 -1.25 -1.0 -0.75 -0.5 -0.25 -0.0 V(VBB) V(QB) V(Q) V(IN) Motorola reserves the right to make changes without further notice to any products herein. Motorola makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does Motorola assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation consequential or incidental damages. "Typical" parameters which may be provided in Motorola datasheetsand/orspecificationscananddovaryindifferentapplicationsandactualperformancemayvaryovertime. Alloperatingparameters,including"Typicals" must be validated for each customer application by customer's technical experts. Motorola does not convey any license under its patent rights nor the rights of others. Motorola products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applicationsintended to support or sustain life, or for any other application in which the failure of the Motorola product could create a situation where personal injury or death may occur. ShouldBuyerpurchaseoruseMotorolaproductsforanysuchunintendedorunauthorizedapplication,BuyershallindemnifyandholdMotorola and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that Motorola was negligent regarding the design or manufacture of the part. Motorola and are registered trademarks of Motorola, Inc. Motorola, Inc. is an Equal Opportunity/Affirmative Action Employer. How to reach us: USA/EUROPE/Locations Not Listed: Motorola Literature Distribution; JAPAN: Nippon Motorola Ltd.; Tatsumi-SPD-JLDC, 6F Seibu-Butsuryu-Center, P.O. Box 20912; Phoenix, Arizona 85036. 1-800-441-2447 or 602-303-5454 3-14-2 Tatsumi Koto-Ku, Tokyo 135, Japan. 03-81-3521-8315 MFAX: RMFAX0@email.sps.mot.com - TOUCHTONE 602-244-6609 ASIA/PACIFIC: Motorola Semiconductors H.K. Ltd.; 8B Tai Ping Industrial Park, INTERNET: http://Design-NET.com 51 Ting Kok Road, Tai Po, N.T., Hong Kong. 852-26629298 AN1404/D *AN1404/D*




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